The continued development of metal-ceramic restorations over the past 30 years has led to almost universal acceptance of this restorative system as the primary esthetic crown and bridge material in dentistry. However, esthetic concerns do exist regarding the opaque nature of the metal substructure and the unnatural appearance that may result. In addition, the esthetics are frequently compromised because of the inadvertent display of the metal or as a result of a graying of the soft tissues surrounding the restoration. Esthetic problems such as these have led to the introduction of a number of all-ceramic (non-metallic) alternatives in the past ten years. However, these ceramic materials are not as strong as the metal-ceramic restorations they are intended to replace. This has continued to limit the applications of all-ceramic dental prostheses (primarily to single tooth anterior restorations) due to their unacceptable clinical failure rate (mechanical fracture). The source and types of mechanical failures associated with dental crown and bridge restorations have not been carefully cataloged and determined. Information currently available on the strength of esthetic prostheses is largely the result of extrapolation of in-vitro studies or basic science information. This project will provide significant new data on the mechanics of in-vivo dental structures. Although research into the strengthening of dental ceramics is ongoing, the basic intraoral mechanisms, origins, and causes of failure have not been determined. This information is fundamental to the rational and logical development of ceramics as a restorative material. The proposed research will utilize fractographic analysis to study clinically failed ceramic crown restorations. This will allow for the first direct measurement of the functional (in-vivo) strength at failure of crown restorations fabricated from a variety of ceramic materials: Dicor(TM), Empress(TM), In-Ceram(TM), and aluminous jacket. The mode, origin, and cause of the fracture will also be determined. In such a manner, the problematical areas associated with fracture of dental ceramic systems will be identified. Once determined, solutions to the failure mechanisms can be suggested which may result in altered crown fabrication, tooth preparation, or cementation system. This will provide critical information for the further development, direction, and improvement of ceramic dental materials.